MG Car Repair: Oil pressure relief valve, pressure relief valve, lhd car

Question
Barrie,I recently had my 1976 MGB engine rebuilt. The mechanic put in a new oil pump but the oil pressure is low, about 50 when starting up and then drops down to about 25 after a few minutes of running.  So I thought I would check the oil pressure relief valve.  The spring was only about 2 3/4 inches long so I ordered a new one because the book said it should be 3 inches long.  The problem I am having is trying to get the valve back in the engine.  There isn't much room to work and the spring has to be pressed in hard in order to get the bolt to screw in.  Is there a way to install this valve?  Do I have to remove the exhaust pipe?  Also, would I do any damage to the engine if I drove it to my mechanic without the pressure relief valve.  His shop is only about two miles away.  Any advice you can give me will be much appreciated.

Answer
The oil pressure relief valve on an MGB is designed to operate at 40psi.  The gauge is calibrated to 100psi, but only to protect the gauge, because cold oil is so thick that it can overwhelm the relief valve.  I would expect a newly reconditioned engine to tick over with a pressure of about 25psi when hot, increasing to 40psi at engine speeds above 1500 rpm.  It is quite normal to see 50psi or even more when the oil has not fully heated up.  So, there is nothing wrong with your oil pressure, but you have removed the cover on the valve, and it is essential that you put it all back before driving the car.  Without a spring, the valve will be open, the oil pressure will be zero, and you will ruin the engine if you drive it 200 yards, let alone 2 miles.  It can be done, but it is tough because the valve cover is in such an awkward location.  If you have a LHD car, that makes it even more difficult because of the steering column.  Maybe it would be easier to put the old spring back in, then go to your mechanic and ask him to fit the longer one.  If you want more pressure, a spacer is available that fits between the spring and the cover, but the spacer makes it even more difficult to re-fit the cover.